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Energy Efficiency and Economic Feasibility of an Absorption Air-Conditioning System Using Wet, Dry and Hybrid Heat Rejection Methods

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Energy Efficiency and Economic Feasibility of an Absorption Air-Conditioning System Using Wet, Dry and Hybrid Heat Rejection Methods University of Windsor Scholarship at UWindsor Mechanical, Automotive & Materials Department of Mechanical, Automotive & Engineering Publications Materials Engineering 11-29-2017 Energy efficiency and economiceasibility f of an absorption air- conditioning system using wet, dry and hybrid heat rejection methods Julia Aman University of Windsor Paul Henshaw University of Windsor David S-K Ting University of Windsor Follow this and additional works at: https://scholar.uwindsor.ca/mechanicalengpub Part of the Energy Systems Commons Recommended Citation Aman, Julia; Henshaw, Paul; and Ting, David S-K. (2017). Energy efficiency and economiceasibility f of an absorption air-conditioning system using wet, dry and hybrid heat rejection methods. International Journal of Environmental Studies. https://scholar.uwindsor.ca/mechanicalengpub/7 This Article is brought to you for free and open access by the Department of Mechanical, Automotive & Materials Engineering at Scholarship at UWindsor. It has been accepted for inclusion in Mechanical, Automotive & Materials Engineering Publications by an authorized administrator of Scholarship at UWindsor. For more information, please contact [email protected]. International Journal of Environmental Studies ISSN: 0020-7233 (Print) 1029-0400 (Online) Journal homepage: http://www.tandfonline.com/loi/genv20 Energy efficiency and economic feasibility of an absorption air-conditioning system using wet, dry and hybrid heat rejection methods Julia Aman, Paul Henshaw & David S.-K. Ting To cite this article: Julia Aman, Paul Henshaw & David S.-K. Ting (2017): Energy efficiency and economic feasibility of an absorption air-conditioning system using wet, dry and hybrid heat rejection methods, International Journal of Environmental Studies To link to this article: https://doi.org/10.1080/00207233.2017.1396073 Published online: 29 Nov 2017. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=genv20 Download by: [24.57.235.99] Date: 29 November 2017, At: 08:34 INTERNATIONAL JOURNAL OF ENVIRONMENTAL STUDIES, 2017 https://doi.org/10.1080/00207233.2017.1396073 Energy efficiency and economic feasibility of an absorption air-conditioning system using wet, dry and hybrid heat rejection methods Julia Aman, Paul Henshaw and David S.-K. Ting Turbulence and Energy Laboratory, Centre for Engineering Innovation, University of Windsor, Windsor, Canada ABSTRACT KEYWORDS In tropical and sub-tropical regions, air-conditioning systems account Absorption; air-conditioning; for the greatest electricity consumption and high water use. Solar- wet-cooling; dry-cooling; driven absorption cooling systems can conveniently reduce electricity hybrid cooling; efficiency; consumption at need. The performance of this cooling system cost depends on the system’s heat rejection. A simulation was performed for a 15 kW single effect ammonia-water absorption cooling system driven by low temperature thermal energy and with three different heat rejection methods (wet cooling, dry cooling, and hybrid cooling). This hybrid cooling system uses wet cooling on the absorber and dry cooling on the condenser. The system performance and economics of the chiller with these cooling methods were evaluated. The analysis showed that a wet cooling system has a higher system performance and water consumption compared to a dry cooling system, which has a high primary energy consumption with no water usage. In hot weather conditions and where there is scarcity of water, hybrid cooling can consume on average 41% less electrical energy than dry cooling and 49% less water than wet cooling and the payback period compared to a wet cooling system can be less than three years. 1. Introduction Downloaded by [24.57.235.99] at 08:34 29 November 2017 In tropical and sub-tropical regions, modern cities are the main consumers of electricity and most of this energy is for air-conditioning systems in buildings. In the United Arab Emirates (UAE), 60% of the total electrical energy is consumed by building air-conditioning systems during summer [1]. Improving the efficiency of existing energy usage and using renewable energy resources are key to protect the environment. Renewable energy integration either alone or in hybrid systems can meet the growing energy demand and provide sustainable energies for the future [2]. For air-conditioning applications, conventional vapour com- pression systems are commonly used, which are driven by electrical energy. This causes stress in the generation and distribution systems during the peak load period in the sum- mer. Thermally driven cooling systems are a sustainable energy technology that provides cooling by replacing electrically driven compressor chillers with thermally driven chillers. CONTACT Julia Aman [email protected] © 2017 Informa UK Limited, trading as Taylor & Francis Group .J. AMAN ET AL 2 They are known to be technically feasible [3]. Solar thermal energy is a suitable option for providing this cooling comfort. For example, Australia, with the highest annual solar radiation in the world, can meet its total energy demand by solar thermal energy using an area approximately equal to its existing rooftops [4]. Thermal absorption cooling systems can be driven by waste heat or solar thermal energy. Such a system consists of a heat driven generator, a condenser, an evaporator, a solution heat exchanger and an absorber. While providing cooling, the condenser and the absorber of the absorption chiller produce heat that must be rejected: which is the same as for the condenser of a traditional vapour compression chiller. The performance of the absorption chiller depends on the heat rejection of the absorber as well as the condenser. Hence, it is crucial to consider efficient heat rejection methods and energy consumption of auxiliaries for the overall primary energy balance of this cooling system [5]. There are various heat rejection methods that can be applied for condenser and absorber cooling in absorption cooling systems. These include evaporative or wet (water) cooling towers, air or dry cooling, hybrid cooling (with both wet and dry cooling), geothermal heat sinks, and night radiative cooling [6]. Kummert et al. [7] compared the system performance and energy cost for a geothermal absorption chiller and a vapour compression chiller for providing space heating and cooling in three different cities in Canada. The system coeffi- cient of performance (COP) is always higher for compression heat pump systems, but where electricity prices are relatively low (Vancouver and Montreal) the life cycle cost is higher for natural gas-driven absorption heat pump systems. Although wet cooling is preferable for better system performance for the heat rejection of the absorber and condenser in an absorption chiller, water consumption is dominant in this method. The statistics of water usage at the California Institute of Technology show that 40% of the water consumption is for the central air-conditioning system in the campus [8]. In most of the arid Southwest USA and subtropical regions where policy and cost require reduced water usage, an air-cooled condenser and absorber are necessary. In cities like Hong Kong, the building density is very high and, because of the climate, cooling is needed throughout the year [9]. The government in Hong Kong does not permit the use of fresh water for heat rejection in building/central air-conditioning applications [10]. But, in hot weather where water is available, both wet and dry cooling methods can be used in parallel in a hybrid system. When a cooling tower is used as a heat rejection method for absorption air-conditioning, the energy needed is accounted Downloaded by [24.57.235.99] at 08:34 29 November 2017 for in the primary energy balance. The effectiveness of dry-cooling and wet-cooling methods is determined by the minimum temperature that each heat rejection method can provide. The wet cooling methods use the evaporation process to reject the heat, based on the wet bulb temperature, whereas dry cooling depends on the ambient dry-bulb temperature [11]. An absorption air-conditioning system can be driven by a single-effect absorption chiller with a generator temperature varying from 60 to 120 °C [12]. The heat rejection for this system can be air-cooled or wet-cooled. As the performance of the absorption chiller depends on the absorber heat rejection, different studies of heat and mass transfer have been performed to improve the absorber efficiency, considering the expected high ambient temperature at the time of air conditioning use [13]. A wet-cooled single effect LiBr-H2O absorption chiller has been studied and the efficiency was found to be higher at a higher dry bulb temperature because of the lower relative humidity at the high dry bulb temperature [14]. Asdrubali and Grignaffini performed an experiment using a single effect LiBr-H2O absorption [15], and found the highest performance at a 70 °C generator temperature when INTERNATIONAL JOURNAL OF ENVIRONMENTAL STUDIES 3 wet-cooled heat rejection was applied. A 34 kW LiBr-H2O absorption chiller integrated with membrane distillation was simulated based on UAE weather conditions and the highest COP was 0.7 during the peak period of summer [16]. Some studies have been carried out for the performance of air-cooled LiBr-H2O absorption chillers [13,17,18]. An ammo- nia-water absorption chiller is suitable
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